Films are often formed on glass to alter some of its physical properties, e.g., radiation reflection. The use of heat-reflecting glass plates as window panes or wall panels in building and vehicles is valuable in avoiding unwanted rise in the interior temperature and reducing the heat load on the interior air conditions. Transparent coatings on glass with high reflectivity and low thermal absorption used in architectural glazing applications allow reasonably high solar performance without the need for heat treatment. The film may also be applied to enhance the color of the glass on which it is applied. From a design perspective, it is important that the film result in a product that is aesthetically pleasing; often a neutral color enhancement and uniform appearance are desired.
One common technique for applying such films to flat glass involves spraying a hot ribbon of glass as it exits the float glass tin bath. A liquid solution of metal compounds which are thermally decomposable by the glass are commonly employed, although powders are often also used. Titanium oxide has long been used as a coating on glass to provide a heat-reflecting glass plate. While titanium oxide exhibits a very reflective appearance, however, it is difficult to produce a highly reflective TiO.sub.2 coating with a uniformly neutral color on the glass, and, pure titanium oxide films on glass are susceptible to some physical and chemical durability issues. Other metals have been included with the titanium to alter its properties. For example, tin has been included in titania coatings to improve durability, however, such prior art coatings have reflectivity which is lower than that desired for many architectural glazing applications.
We have now unexpectedly found that by using a titanate, preferably tetrabutyl titanate, as the source of titanium, and a tin compound, preferably dibutyltin-diacetate, in a mixture combined with an anhydrous organic liquid, we can produce an oxide film of titanium and tin which has excellent chemical durability and a unexpected high reflectivity. Use of the titanate allows for incorporation of relatively high amounts of tin oxide in the film while yet providing a highly reflective film. This mixture produces a film exhibiting a very smooth surface, exceptionally neutral appearance and excellent chemical and physical durability. These and other features of the present invention will be discussed in detail below.